Pending U.S. patent application Ser. No. 304,093 to Mahoney and Benwood and U.S. Pat. No. 4,232,961 show multicolor imaging apparatus in which three or four imaging members are separately charged, exposed and toned to create toner images in different colors and those toner images are transferred in registration to an intermediate web from which they are transferred to a receiving sheet. Apparatus with separate imaging members for creation of separate color toner images is many times faster than present commercial devices in which the images are formed consecutively on a web or drum photoconductor.
As pointed out in the Mahoney et al application, the web intermediate has the advantage of lending itself to single-pass duplexing of consecutive multicolor images. Another advantage of web imaging members per se is that they can be trained around a small diameter roller to assist in separating a receiving sheet.
A number of other references show separate imaging members which create separate color toner images and transfer them directly to a receiving sheet. See for example U.S. Pat. Nos. 4,464,501; 4,162,843; 4,662,739; 4,690,542 4,809,037; and 4,835,570. In U.S. Pat. No. 4,580,889 the transfer sheets are presented to the imaging members by attaching them to the surface of a drum rather than a moving web which is shown in rest of the above references.
Maintenance of cross-track and in-track registration between toner images is a serious challenge in designing and manufacturing color apparatus having a web imaging member. In-track registration is controlled in the Mahoney et al structure by a sprocket and perforation system which automatically adjusts for variations in the speed and manufacture of the web. Reasonably good cross-track registration is obtained since the web has a tendency to follow itself over short distances reasonably well. However, for highest quality work even complex web tracking systems are unable to prevent some noticeable cross-track misregistration. This becomes more critical as materials and exposure systems are improved and provide higer resolution.
U.S. Pat. Nos. 4,378,154; 4,624,549; 4,497,570; and 3,820,985 show an electrophotographic imaging apparatus in which a protoconductive web is trained around a large roller or drum and at least one or more small rollers. The small roller has the advantage shown, for example, in 4,378,154, of assisting in separation of a receiving sheet. The large roller or drum helps maintain good separation between the image forming stations and the electrophotographic member. FIG. 4 of U.S. Pat. No. 3,820,985 shows such a drum-web structure in a color imaging device. Registration problems are not addressed or corrected in this structure.